Isolate context.

• Define policies reflecting contexts, styles, and conventions.
• Policies impact many, otherwise unrelated components.
• Conformance to common policies enhances composibility and eliminates the need for glue code.

Examples

• Responsibility for handling preconditions. Alternatives include those where the component is responsible for handling bad messages, and where the client is responsible for ensuring preconditions.
• Actions occuring under failed preconditions. Alternatives include raising exceptions, setting failure flags, inaction, and delaying action until the precondition is satisfied.
• Storage management. Alternatives include garbage collection, reference-counting, split component-client protocols.
• Object generation. Alternatives include random construction, ``factories'' that manage construction of related components, and centralized services.
• Persistence. Alternatives include reliance on central databases, use of proxies, and tools.
• Coding standards.